Robot Structural Analysis

## Robot Structural Analysis

Active Contributor
Posts: 47
Registered: ‎05-14-2012
Message 1 of 18 (1,085 Views)

# tutorial or exaple for machine foundation

1085 Views, 17 Replies
07-11-2012 06:54 AM

Does anyone have a tutorial or example for RSA, how to design concrete blocks or pedestals for steam or  gas turbines or smth similar. Modal,time history analysis or harmonis (FRF), how to apply the dynamic forces that act in the neutral axisof the turbine which is above the foundations, what load combinations to use, what type of mashing is the best chooise in this case.

Thanks

Valued Mentor
Posts: 606
Registered: ‎09-07-2011
Message 2 of 18 (1,067 Views)

# Re: tutorial or exaple for machine foundation

07-12-2012 04:55 AM in reply to: alb2
Product Support
Posts: 424
Registered: ‎06-23-2008
Message 3 of 18 (1,061 Views)

# Re: tutorial or exaple for machine foundation

07-12-2012 05:56 AM in reply to: tony.ridley

1/ depending on soil data and necessity to consider deformation of foundation or treating it as rigid body it is possible to model it as

- node with added mass and elastic support

- panel on elastic supports

- solid on elastic supports

2/ eccentricity between foundation and turbine can be modeled using rigid links

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Regards,

Pawel Pulak
Active Contributor
Posts: 47
Registered: ‎05-14-2012
Message 4 of 18 (1,055 Views)

# Re: tutorial or example for machine foundation

07-12-2012 06:14 AM in reply to: pp2008

can you please show in a picture or I a small model how to model the eccentricities with rigid links?

Thanks

Product Support
Posts: 424
Registered: ‎06-23-2008
Message 5 of 18 (1,042 Views)

# Re: tutorial or example for machine foundation

07-12-2012 08:59 AM in reply to: alb2

The screen capture below shows some example when modeling by solid. Top (master) node corresponds to the center of mass of the turbine. Bottom nodes correspond to the connection of the turbine with the block. Of course the distribution of these nodes corresponds to real geometry of turbine and details of connection.

In case of rigid links connected to solid it will be necessary to activate RLINK algorithm for rigid links in Job Preferences>Structure Analysis

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Regards,

Pawel Pulak
Active Contributor
Posts: 47
Registered: ‎05-14-2012
Message 6 of 18 (980 Views)

# Re: tutorial or example for machine foundation

07-18-2012 06:28 AM in reply to: pp2008

Mr. Pulak,

I am trying to model the following as in picture 1, as you explained in the previous email, and I am getting the following error,picture 2. What am I doing wrong?

Thanks

Product Support
Posts: 424
Registered: ‎06-23-2008
Message 7 of 18 (963 Views)

# Re: tutorial or example for machine foundation

07-18-2012 07:11 AM in reply to: alb2

Solid elements have no degrees of freedom (stiffness) in rotation. So if you have defined rigid links with only pairs of nodes (one master and one slave) these rigid links can rotate about nodes belonging to solids - at the bottom ends of rigid links shown on your screen capture.

One of the methods to avoid it is to define rigid links with at least 3 non-collinear slave nodes to connect to solid in 3 points - like below:

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Regards,

Pawel Pulak
Active Contributor
Posts: 47
Registered: ‎05-14-2012
Message 8 of 18 (905 Views)

# Re: tutorial or example for machine foundation

07-23-2012 02:31 AM in reply to: pp2008

Hi,

how can isolated nodes with attributes be included in the mesh? I am trying with Emitters, but no luck, is there a meshing option that includes all nodes where node forces are applied before meshing?

And also getting the following warning:It is neccesary to divide tapered bar to calculation elements for nonlinear analysis.

What does it mean? since i have no bars in the model ( its a concrete block) and how can it it be done?

Thanks

Product Support
Posts: 424
Registered: ‎06-23-2008
Message 9 of 18 (879 Views)

# Re: tutorial or example for machine foundation

07-23-2012 06:53 AM in reply to: alb2

If FE mesh is not frozen it is enough to run analysis and during model generation FE mesh will be adapted to new surface nodes.

In case of local mesh generation (as in the video available there: http://screencast.com/t/tNiJTBWiZk ) FE mesh is adapted to new surface nodes for unfrozen and  frozen FE meshes.

Above remarks are valid for solids meshed using standard tetrahedral FE mesh generation.

In case of mapped meshing of solids generated using extrude or revolve commands adapting mesh is not possible for side faces - but your screen capture suggests that you do not use this feature.

As concerns the warning related to tapered members it is not justified and can be ignored.

Best regards,

Pawel Pulak
Active Contributor
Posts: 47
Registered: ‎05-14-2012
Message 10 of 18 (844 Views)

# Re: tutorial or example for machine foundation

07-24-2012 03:55 AM in reply to: pp2008

Mr Pulak,

In order to obtain a) steady state response of a concrete block on which a machine is operating with a xx frequency:

1) calculated the right modal frequencies with all dead loads converted into mass

2) calculated the dynamic forces and moments ( in phase and out of phase in all directions) acting to the centre of concrete base area, and applied these forces to this point as a new load case (in phase Y).

3) the load case (in phase Y) chanced to a harmonic analysis with excitation frequency of the machine ( 50 hz in this case)

4) results - displacement - for case 5 ( in phase Y)

b) transient amplitude

same as a) till point 2) but instead of harmonic analysis will be Harmonic (FRF) from 0.5-50 Hz ( this time for out of phase Y)

3) results- advanced- FRF tables or diagrams

Please confirm if the above steps are correct

Thanks

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